The startle response will be studied in normal 3, 4, 5, and 8 year old children and in adults in order to obtain quantitative neurophysiologic data on the maturation and development of this important brain stem reflex. Startle response components to be recorded include EMG from orbicularis oculi and neck muscles and selected antagonistic flexors and extensors, the blink reflex, change in heart rate, and evoked and background EEG activity. All response components will be recorded quantitatively by a computer system which will also control the time of administration of stimuli according to the prestimulus state of the subject. Additional control over the prestimulus state will be obtained by the use of a lead stimulus which in adults has been found to increase the predictability of responses to startle stimuli. The significance of this investigation is the increase in understanding of the normal maturation and development of subcortical brain mechanisms that may be involved in the learning process. Thus, this study of normative responses may have application to developmental and learning disorders.